tls.go

package butlerd

import (
	"bytes"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/rsa"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"fmt"
	"math/big"
	"net"
	"os"
	"time"

	"github.com/pkg/errors"
)

type TLSState struct {
	Config       *tls.Config
	CertPEMBlock []byte
}

func MakeTLSState() (*TLSState, error) {
	ts := &TLSState{}

	var keyPEMBlock []byte
	var certPEMBlock []byte

	priv, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	// Generate cryptographically strong pseudo-random between 0 - 2^130
	// (We need a unique serial number otherwise Chromium on Linux will
	// reject any cert beyond the first with net::ERR_SSL_SERVER_CERT_BAD_FORMAT)
	max := new(big.Int)
	max.Exp(big.NewInt(2), big.NewInt(130), nil).Sub(max, big.NewInt(1))
	serial, err := rand.Int(rand.Reader, max)
	if err != nil {
		return nil, err
	}

	template := x509.Certificate{
		SerialNumber: serial,
		Subject: pkix.Name{
			Organization: []string{"itch corp."},
		},
		IPAddresses: []net.IP{
			net.IPv4(127, 0, 0, 1),
			net.IPv6loopback,
		},
		DNSNames:  []string{"localhost"},
		NotBefore: time.Now(),
		NotAfter:  time.Now().Add(time.Hour * 24 * 365),

		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
		IsCA: true,
	}

	derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, publicKey(priv), priv)
	if err != nil {
		return nil, errors.WithStack(err)
	}
	certOut := &bytes.Buffer{}
	err = pem.Encode(certOut, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes})
	if err != nil {
		return nil, errors.WithStack(err)
	}
	certPEMBlock = certOut.Bytes()

	keyOut := &bytes.Buffer{}
	err = pem.Encode(keyOut, pemBlockForKey(priv))
	if err != nil {
		return nil, errors.WithStack(err)
	}
	keyPEMBlock = keyOut.Bytes()

	cert, err := tls.X509KeyPair(certPEMBlock, keyPEMBlock)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	ts.CertPEMBlock = certPEMBlock
	ts.Config = &tls.Config{
		Certificates: []tls.Certificate{cert},
		NextProtos:   []string{"h2"},
	}

	return ts, nil
}

func publicKey(priv interface{}) interface{} {
	switch k := priv.(type) {
	case *rsa.PrivateKey:
		return &k.PublicKey
	case *ecdsa.PrivateKey:
		return &k.PublicKey
	default:
		return nil
	}
}

func pemBlockForKey(priv interface{}) *pem.Block {
	switch k := priv.(type) {
	case *rsa.PrivateKey:
		return &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(k)}
	case *ecdsa.PrivateKey:
		b, err := x509.MarshalECPrivateKey(k)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Unable to marshal ECDSA private key: %v", err)
			os.Exit(2)
		}
		return &pem.Block{Type: "EC PRIVATE KEY", Bytes: b}
	default:
		return nil
	}
}